The separation and capture of particles or aerosols from air or other fluid streams are of concern in two contexts: first, in determining the type and concentration of such particles/aerosols and, second, in cleansing the fluid stream for subsequent use. For example, the detection or extraction of airborne biological or chemical warfare agents, biological contamination in confined spaces, such as aircraft or hospitals, or industrial pollutants (either in ambient air or in smokestacks) may be required in various scenarios.
Much effort has been expended in the past in the detection and extraction of particles or aerosols, generally in air or other gaseous streams. Impactors have been used for collecting aerosol particles for many decades. In their typical embodiments, a stream of gas containing particles is accelerated toward an impactor plate. Due to their inertia, the particles hit the impactor plate and are collected there while the gas is deflected to the side. Therefore, only larger particles with greater mass and inertia are collected on the impactor plate for separation and/or detection, while smaller particles with less mass and inertia are carried away by the gas stream.
However, a significant cause of inaccuracy in such impactors results from the deposition of particles on surfaces of the impactor plate other than the intended collection surfaces. Additionally, particles may bounce from the collection surfaces upon impact and reentrain in the gas stream.
Both a efficiency particulate airfilter (HEPA) and/or ELECTRET.RTM. fiber filter can be used as a fluid filter to capture particles/aerosols. These filters, however, typically create a large pressure drop within the filter, which may hinder efficient flow of a fluid stream and, thus, separation and collection of particles entrained in the fluid stream, as well as capacity. Aerogels have been used to overcome the pressure drop problem but they, like other materials comprising fibrous materials, tend not to allow easy extraction of the particles entrapped therein for subsequent collection or analysis.
A need exists for impactors that efficiently separate and collect particles thereon, and retain the collected particles without immediately releasing them back into a fluid stream. Preferably, such impactors do not cause a large pressure drop and, also, allow for easy extraction of the particles therefrom, subsequent to the particle deposition onto the impactors.